1. Field of the Invention
This invention relates to modified polyphenylene ether resins having improved flow properties and, in particular, it relates to modified polyphenylene ether resins incorporating a polybrominated higher alkylbenzene and a flame retardant enhancer such as antimony trioxide.
2. Description of the Prior Art
Traditionally, most flame retardants, although efficient in their function of retarding the rate of combustion in a resin system, have a tendency to affect adversely one or more key properties of the resin. For example, many flame retardant additives tend to reduce impact strength of the resin; to migrate from the resin composition, resulting in a phenomena known as "bloom"; to volatilize from the resin composition; to plasticize the resin composition adversely, thus lowering the heat deflection temperature, etc.
It is therefore essential that flame retardant agents be specifically tailored to the resin system so that, in addition to its role as a flame retardant, the agent will additionally enhance the desirable characteristics of the resin composition. Those skilled in the art well known that the selection of such an application-specific flame retardant is unpredictable at best. Thus, even through a given agent may exhibit utility in a particular resin system, that is no guarantee that this agent will have any use at all with other resins.
Modified polyphenylene ether ("MPPE") resins are a well known class of thermoplastic resins which combine relatively high impact, excellent thermal stability, low water absorption and a low degree of flammability. These resins are produced by alloying polyphenylene ether polymers with alkenyl aromatic resins such as impact polystyrene. The terms "modified polyphenylene ether" and "MPPE" are used herein to refer broadly to all of these alloyed resins.
Even though modification with polystyrene does increase ease of molding of unmodified polyphenylene ethers, such MPPE resins often exhibit far from ideal flow properties. Thus further flow modification is usually required to provide resins that are readily moldable at moderate temperatures.
Although unmodified polyphenylene ethers exhibit substantial inherent flame resistance, modification with impact polystyrene significantly increases their flammability. Since MPPE resins find increasing application in electrical and electronic equipment and appliances, a high level of flame retardancy is usually required.
Aromatic phosphate esters have been used for some time to increase the flame retardancy of MPPE resins. As noted in U.S. Pat. No. 4,579,901, Table 1, when sufficient amounts of the esters are added to provide a good degree of flame retardancy, the compositions are also plasticized, resulting in improved melt flow behavior. However, such compositions also exhibit a serious loss of heat resistance, a marked disadvantage. Another problem is that some of the volatile fluid phosphate esters often migrate to the surface during molding, accumulating as droplets near the molding vents. This effect, known in the trade as "juicing," is not only objectionable from an appearance standpoint, but it may also result in stress cracking. The plastic part as molded may be under stress and the accumulated liquid phosphate ester can induce cracking. For example, see U.S. Pat. No. 4,503,178, column 1, line 65, to column 2, line 11.
Underwood, et al. U.S. Pat. No. 3,850,882 disclose a three component flame retardant additive system for polyolefins, especially polypropylene, consisting of
(a) among other halogenated aromatic compounds, a halogenated alkyl benzene of the formula ##STR1## where X may be Cl or Br; and Y is a hydrocarbon of 1-20 carbon atoms; a is an integer from 0 to 3; and n is an integer from 3 to 6.
(b) stannic oxide;
(c) a bis-phenylalkylene hydrocarbon.
The patent does not suggest that such a flame retardant mixture has any utlity in MPPE resins, let alone that the halogenated alkylbenzene would have any such use.
Rueter, et al. U.S. Pat. No. 4,129,551 discloses nonflammable polyester compositions incorporating a phosphorus-containing, multiple component flame retardant additive consisting of:
(a) a triarylphosphine oxide or an aryl or alkyl ester of an arylphosphinic acid;
(b) a nuclear brominated alkylbenzene; and
(c) customary auxiliary agents and additives.
Polyester compositions based on such agents contain 0.5-10% by weight of bromine and 0.1-2% by weight of phosphorus. Among the nuclear brominated alkylbenzenes described were a compound of the following formula: ##STR2## where x=2 to 5, y and z each are zero or an integer from 1 to 17 and sum of y+z is an integer between 7 and 17.
Mixtures of such agents are also suggested. There is no disclosure that the additive mixture has any utility in MPPE resins or that the nuclear brominated alkylbenzene may be so-used alone for that or any other purpose.
Therefore, it is a principal object of this invention to provide modified polyphenylene ether compositions having flame retardancy and improved flow properties during molding.
Another objective of this invention is to provide modified polyphenylene ether resin compositions incorporating a superior flame retardant agent.
Yet a further object is to utilize polybrominated higher alkylbenzenes as flame retardant melt flow modifiers for MPPE resin compositions.
Another object of this invention is to provide such flame retardant compositions which have reduced amounts of the flow enhancer that accumulates on the surface of molded parts.